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Mefenamic acid

This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by Public Health England on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during pregnancy.

What is it?

Mefenamic acid (Ponstan®) is a non-steroidal anti-inflammatory drug (NSAID) that is prescribed to treat arthritic pain, pain after an operation, and heavy and painful periods. This leaflet summarises the scientific studies relating to the effects of mefenamic acid on a baby in the womb.

Is it safe to take mefenamic acid in pregnancy?

Use of mefenamic acid during pregnancy is not advised unless prescribed by your doctor, especially if you are 30 or more weeks pregnant. For some women with certain illnesses, mefenamic acid may be prescribed before 30 weeks of pregnancy. For most women paracetamol is usually recommended to control pain or fever during pregnancy. If paracetamol does not control your pain it is important that you ask your doctor for advice before taking mefenamic acid or any other NSAID. Your doctor is the best person to help you decide what is right for you and your baby.

This leaflet summarises the scientific studies relating to the effects of mefenamic acid on a baby in the womb. It is advisable to consider this information before taking mefenamic acid if you are pregnant.

What if I have already taken mefenamic acid during pregnancy?

There is no strong scientific proof that taking mefenamic acid before week 30 of pregnancy will harm a baby in the womb. However, if you have taken or are taking any medicines, it is always a good idea to let your doctor know that you are pregnant so that you can decide together whether you still need the medicines that you are on, and to make sure that you are taking the lowest dose that works.

If you have taken mefenamic acid after week 30 of pregnancy it is important that you let your doctor or midwife know straight away as your baby’s wellbeing in the womb will need to be assessed.

Can taking mefenamic acid in pregnancy cause miscarriage?

It is unclear whether taking mefenamic acid in early pregnancy increases the chance of having a miscarriage. Some studies of groups of women who took any type of NSAID during pregnancy have shown that these women are more likely to have a miscarriage than women who have not taken an NSAID. However, NSAIDS are sometimes used to treat illnesses that carry a higher risk of miscarriage, which may explain this finding. No studies have examined miscarriage rates in women specifically taking mefenamic acid. Further research is required before we can say whether taking mefenamic acid during pregnancy increases the risk of miscarriage.

Can taking mefenamic acid in pregnancy cause my baby to be born with birth defects?

A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that some medicines are known to cause birth defects.

There are no studies that have specifically investigated whether taking mefenamic acid during early pregnancy causes birth defects in the baby.

Most studies of groups of women who took any type of NSAID during the first three months of pregnancy have not shown that these women were more likely to have a baby with a birth defect than women who didn’t take NSAIDs. A small number of studies have suggested possible links between taking NSAIDs in early pregnancy and various specific birth defects. However, none of these studies provide enough evidence to prove that NSAIDs cause any type of birth defect. Diclofenac might also affect an unborn baby differently to other NSAIDs. More information needs to be collected about pregnant women specifically taking mefenamic acid.

What problems can taking mefenamic acid after 30 weeks of pregnancy cause in my baby?

Premature closure of the ductus arteriosusBefore birth, a blood vessel in the baby called the ductus arteriosus needs to stay open to supply the baby in the womb with nutrients and oxygen from the mother. The ductus arteriosus closes just after birth to allow the baby’s blood to flow through its lungs once it starts breathing. Premature closure of the ductus arteriosus is the medical term used to describe this blood vessel closing before it is supposed to.

Taking NSAIDs after 30 weeks of pregnancy can cause the ductus arteriosus to close while the baby is still in the womb, and the baby may then need to be delivered early. Although this effect has not been shown with mefenamic acid, very few women taking it after 30 weeks of pregnancy have been studied. It is therefore important to contact your doctor or midwife straight away if you have taken any NSAID after 30 weeks of pregnancy, especially if you have taken several doses or more than the recommended dose.

Persistent pulmonary hypertension of the newborn (PPHN)PPHN or persistent pulmonary hypertension of the newborn occurs when a newborn baby’s lungs do not adapt to breathing outside the womb. It is thought to be linked, in some cases, to early closure of the ductus arteriosus (see above). PPHN only affects around 1 or 2 out of every 1,000 newborn babies in the general population but is important as it can be serious.

Although one study has shown a link between PPHN and taking NSAIDs during pregnancy, another study did not show a link. There have been no specific studies of mefenamic acid and more research is therefore needed to investigate whether taking mefenamic acid in the third trimester increases the risk of PPHN in the baby.

Oligohydramnios (reduced fluid around the baby)There have been no specific studies of whether mefenamic acid causes oligohydramnios (where there is too little amniotic fluid in the sac around the baby). However, use of other NSAIDs after 30 weeks of pregnancy has been linked to oligohydramnios, which can cause a number of complications, including:

• The baby’s lungs being under-developed (because inhaling amniotic fluid while in the womb helps to expand and develop the lungs).

• The baby’s bladder being under-developed (because urine expands and develops the bladder).

• The baby’s skull and leg bones being misshapen and the baby having ‘flattened’ facial features (because amniotic fluid ‘cushions’ the baby in the womb).

• Compression (squashing) of the umbilical cord, which may result in reduced blood flow from the mother to the baby in the womb.

If you have taken mefenamic acid after 30 weeks of pregnancy your doctor may wish to check your amniotic fluid levels by ultrasound scan.

Use of mefenamic acid during the third trimester of pregnancy should be avoided. Please discuss any concerns that you may have with your doctor.

Can taking mefenamic acid in pregnancy cause preterm birth or my baby to be small at birth (low birth weight)?

No studies have investigated whether women in the general population taking mefenamic acid are at increased risk of preterm birth or of having a low birth weight baby, although studies of pregnant women taking any NSAID have not shown that the risks of these are increased. We do not, however, know whether mefenamic acid might affect a baby in the womb differently to other NSAIDs and so more information on women taking mefenamic acid in pregnancy needs to be collected.

A single study of women who were considered to be at high risk of giving birth early for specific reasons showed that those taking mefenamic acid were less likely to have a preterm birth (before 37 weeks of pregnancy) or to have a low birth weight baby (<2500g) than high risk women who did not take mefenamic acid. These results are only relevant to women with certain health conditions. Do not take mefenamic acid in pregnancy unless advised to do so by your doctor.

Can taking mefenamic acid in pregnancy cause learning or behavioural problems in the child?

A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

There is no known link between taking mefenamic acid in pregnancy and learning or behavioural problems such as attention deficit hyperactivity disorder (ADHD) or autism spectrum disorder in the child. There are, however, no scientific studies that have specifically investigated a link with these problems.

Will my baby need extra monitoring during pregnancy?

Most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects as part of their routine antenatal care. Taking mefenamic acid before 30 weeks of pregnancy would not normally require extra monitoring of your baby.

If you have taken mefenamic acid after 30 weeks of pregnancy you may need extra scans or monitoring of your baby.

Are there any risks to my baby if the father has taken mefenamic acid?

We would not expect any increased risk to your baby if the father took mefenamic acid before or around the time your baby was conceived.

Who can I talk to if I have questions?

If you have any questions regarding the information in this leaflet please discuss them with your health care provider. They can access more detailed medical and scientific information from www.uktis.org.

General information

Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks. They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.

Medicines use in pregnancy

Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby. There are, however, some medicines that can harm a baby’s normal development. How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.

If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.

When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.

Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider.It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.

www.medicinesinpregnancy.org

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.